It is known in the art to manufacture N-alkylpiperazines from piperazine and a carbonyl compound, in the presence of hydrogen, over a nickel catalyst.
Usually, the piperazine is prepared from ethylenediamine, aminoethylethylenediamine, monoethanolamine or diethanolamine by reaction with ammonia over a metal-type hydrogenation-dehydrogenation catalyst, such as, for example nickel or another metal.
The choice of the route is influenced to some extent by the other nitrogen derivatives the producer desires to manufacture. See Kirk-Othmer: Encyclopedia of Chemical Technology, 3rd ed., Vol. 2, p. 298, John Wiley, N.Y.
The reaction can be generally represented as follows: ##STR1##
It is also well-known that the reaction of piperazine with carbonyl compounds is not selective and, after hydrogenation of such adducts, the removal of solid piperazine by distillation is tedious.
Piperazine is a solid which melts at 109.6.degree. C. and boils at 148.5.degree. C. Because it is a solid that melts close to its boiling point it is very difficult to isolate it with a high degree of purity by distillation. In the commercial preparation setting, this means that all the lines must be heated so that piperazine does not freeze up in the distillation procedure.
Another problem is that much of the piperazine does not react. For example, in the preparation of isobutylpiperazine from isobutyraldehyde and piperazine, unreacted piperazine will interfere with the isolation and purity of the final product. This is usually addressed by using an excess of isobutyraldehyde, which results in reduced yields of the desired product. ##STR2##
It does not appear that it has been suggested anywhere in the art to manufacture N-alkylpiperazine in a manner which bypasses the production and isolation of piperazine.
Such a method would represent a significant advance in the art because it would reduce costs in a commercial operation due to the fact it would not be necessary to heat distillation lines in conjunction with isolation of the piperazine. Also the use of an excess of isobutyraldehyde would not be necessary.
In the instant invention a carbonyl compound such as isobutyraldehyde is reacted with aminoethylethanolamine over a hydrogenation catalyst to give alkylpiperazine.